David Sims dispelled the idea that basking sharks hibernate on the North Sea floor.
For nearly 50 years, basking sharks were thought to disappear into deep water during winter and remain dormant on the seabed. Their seasonal absence from coastal surface waters seemed to support that explanation, especially because the species is slow-moving and can reach enormous sizes.
Beginning in the 1990s, marine biologist David Sims combined long-term field observations with archival and satellite tagging. The tracking showed that basking sharks remained active in winter, moving through deeper shelf and offshore waters rather than entering true hibernation. They followed concentrations of overwintering zooplankton, their principal food.
The common mix-up is treating disappearance from the surface as proof of dormancy. Basking sharks can dive to depths approaching 900 metres and are less visible in winter, but they continue seasonal movements and feeding. Sims’s work also helped establish that these sharks are migratory, filter-feeding animals rather than inactive winter residents of the seabed.